The 1st African-derived rock formations

The Geological Formation of Calitzdorp and Its Environs: A Fascinating Tale from the Cretaceous Period

More fossilized dragon than rock, we passed within harpooning distance of one of my favourite geological formations. Gnarled, sinewy, pock-marked from erosion and studded with shards of quartzite pebbles. These are the hills of Calitzdorp which have seen far more interesting circumstances than any Hobbit tale! This formation occurred during the Cretaceous Period, a time when the Earth was dramatically reshaped by the forces of nature.

The Cretaceous Period: A Time of Dramatic Transformation

Around 145 million years ago, during the early Cretaceous Period, the ancient supercontinent Gondwana began to break apart. This geological event led to the separation of the landmasses that would eventually form Africa, South America, Australia, India, and Antarctica. Africa, for the first time: stood alone.

The climate during this time was warm and humid, characterized by lush vegetation and the dominance of large dinosaurs. As the Earth's crust stretched and split apart, it underwent significant changes. Violent earthquakes, torrential rains, and rock fracturing were commonplace as the planet's surface was torn apart, giving birth to new landforms. These tectonic forces were responsible for the formation of elongated basins, such as the Oudtshoorn Basin in the Eastern Klein Karoo. This basin, which extends as far west as Calitzdorp, was shaped by the deep fracture of the Earth's crust that ran from east to west along the base of the Swartberg Mountains.

The Role of Faults and River Systems

Central to the formation of the Oudtshoorn Basin was the Kango Fault, a major geological feature running along the northern margin of the basin. This fault not only caused the floor of the basin to subside but also influenced the region's river systems. Uplifted highlands, such as the Gamkasberg and Rooiberg, acted as sources for rejuvenated rivers that flowed into the basin. These rivers carried vast amounts of debris, including scree and rock fragments from the Table Mountain Sandstone and Quartzite that surrounded the Little Karoo. As these rocks tumbled from the mountains above they got rounded on their journey and reduced in size to rocks and pebbles.

As these rivers deposited their load, they gave rise to the Buffelskloof Formation—once known as the Enon Conglomerates—a crucial geological feature that marks the first truly African sediments. These sediments, laid down during the formation of the African continent, consist primarily of rounded cobbles and pebbles embedded in silica-rich gravels. Additionally, the angular rock fragments found on the surrounding slopes are known as Breccias, providing further evidence of the powerful geological forces at play.

The Formation of the Red Stone Hills

One of the most striking features of these mountains are its vivid red sediments. The red hue of the landscape is a result of hematite, an iron-rich mineral that oxidized in the warm, humid conditions of the Cretaceous. The oxidation process turned the sediments into the reddish color that is visible today. These red gravel sediments originally formed the northern margin of the Oudtshoorn Basin. Over the course of 100 million years of erosion, these sediments have been worn down, leaving behind isolated koppies (small hills) that stretch in a band from De Rust to Calitzdorp.

Weathering and erosion played a critical role in shaping the Red Stone Hills into the sleeping dragons of today. The outer crust of these sediments, which initially eroded quickly, became more resistant over time. This led to the formation of natural features such as caves, overhangs, and, most notably, the stunning Hole-in-the-Wall.

Fossils and the Challenges of Dating

Despite the absence of fossils in the Red Stone Hills themselves sure to the high energy of the system and oxygen-rich environment that is not conducive to fossil-formation, there are some notable examples of relict species that have survived since the time of the Cretaceous. These species, which have remained virtually unchanged for over 100 million years, serve as living links to the distant past. The cycad species, Encephalartos horridus, is still found in secluded valleys within the region, while an ancient fish species continues to inhabit the perennial streams near the Swartberg foothills close to Calitzdorp. These living fossils provide a glimpse into a world that existed long before the region's human inhabitants.

A Window into Earth’s Ancient Past

The geology of Calitzdorp and its surrounding regions offers a fascinating glimpse into the Earth's distant past. Nowadays, all these years later, these remnant humpbacks are home to an array of renosterveld, fynbos elements, and bulbs some of which have uniquely developed and survived on these mountains for millions of years. But what blows my mind is that the same principles of erosion and subsequent deposition of rocks are still happening today. Thus these mountains are currently being eroded and deposited for at least a third traceable cycle, and some of these rocks will be reburied for a fourth time to be re-exposed several hundred million years from now.
1) sediment washes to form some proto-mountain.
2) these are washed down and deposited as layers of Table Mountain sandstone.
3) this TMS washes down and forms the Buffelskloof conglomerate and breccia.
4) these pebbles will wash downriver to our present-day coast as sand to be consolidated one day into new rock.

I wish to thank Geoff Wyatt-Goodall for consolidating the information that formed the basis for my research into this formation. https://www.swartbergcircleroute.co.za/project/…Read more